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BUG: KCSAN: data-race in do_syslog / log_store

write to 0xffffffff89513200 of 8 bytes by task 3258 on cpu 0:
 log_store+0x7a2/0x7d0 kernel/printk/printk.c:672
 log_output kernel/printk/printk.c:1932 [inline]
 vprintk_store+0x5ba/0x700 kernel/printk/printk.c:1983
 vprintk_emit+0x114/0x4f0 kernel/printk/printk.c:2011
 vprintk_default+0x24/0x30 kernel/printk/printk.c:2047
 vprintk_func+0x13d/0x140 kernel/printk/printk_safe.c:393
 printk+0x62/0x82 kernel/printk/printk.c:2078
 buffer_io_error fs/buffer.c:129 [inline]
 end_buffer_async_read+0x2f1/0x330 fs/buffer.c:259
 end_buffer_async_read_io+0x15a/0x170 fs/buffer.c:335
 end_bio_bh_io_sync+0x6f/0x90 fs/buffer.c:3021
 bio_endio+0x28a/0x370 block/bio.c:1449
 req_bio_endio block/blk-core.c:259 [inline]
 blk_update_request+0x535/0xbd0 block/blk-core.c:1577
 blk_mq_end_request block/blk-mq.c:562 [inline]
 blk_mq_dispatch_rq_list+0x57a/0xd10 block/blk-mq.c:1406
 __blk_mq_do_dispatch_sched block/blk-mq-sched.c:201 [inline]
 blk_mq_do_dispatch_sched+0x370/0x610 block/blk-mq-sched.c:214
 __blk_mq_sched_dispatch_requests+0x1fd/0x2a0 block/blk-mq-sched.c:325
 blk_mq_sched_dispatch_requests+0x9f/0x110 block/blk-mq-sched.c:356
 __blk_mq_run_hw_queue+0xee/0x1c0 block/blk-mq.c:1534
 blk_mq_run_work_fn+0x3d/0x50 block/blk-mq.c:1812
 process_one_work+0x3e1/0x9a0 kernel/workqueue.c:2269
 worker_thread+0x665/0xbe0 kernel/workqueue.c:2415
 kthread+0x20d/0x230 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

read to 0xffffffff89513200 of 8 bytes by task 8403 on cpu 1:
 do_syslog+0x2e4/0x1480 kernel/printk/printk.c:1561
 kmsg_read+0x7a/0xa0 fs/proc/kmsg.c:40
 pde_read fs/proc/inode.c:306 [inline]
 proc_reg_read+0xde/0x1a0 fs/proc/inode.c:316
 vfs_read+0x16d/0x5e0 fs/read_write.c:479
 ksys_read+0xce/0x180 fs/read_write.c:607
 __do_sys_read fs/read_write.c:617 [inline]
 __se_sys_read fs/read_write.c:615 [inline]
 __x64_sys_read+0x3e/0x50 fs/read_write.c:615
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 8403 Comm: in:imklog Not tainted 5.9.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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